S.J. Gould wrote a series of interesting articles (chapters 22-24 in Ever Since Darwin) about the ratio of body mass to brain mass among animal species. Bigger animals have bigger brains (of course) but the ratio is getting smaller: a human's brain is smaller than an ant's relative to body size. Gould conjectures that this is due to volume to surface area ratio: since volumes (and therefore masses) increase faster than surface areas, an ant has a larger surface area to body mass ratio. Therefore, the ant needs a relatively bigger brain to control and sense its body surface area, with its appendages, nerves, etc.

Question: this explanation sounds reasonable, but Gould provides no evidence. Does anyone know of evidence to support that hypothesis, or of other hypotheses?